Sodium benzoate is a preservative that has been widely used for decades in commercially available foods and carbonated drinks, but has recently become the focus of renewed interest.

It is the sodium salt of benzoic acid, which is found naturally in berries. The preservative made headlines in May 2007 when a British researcher suggested that it can turn off key parts of DNA, an effect that could lead to cirrhosis of the liver, Parkinson's disease and other degenerative disorders.

Peter Piper, a professor of molecular biology and biotechnology at Britain's Sheffield University, warned that sodium benzoate can severely damage DNA in the mitochondria (the "power stations" inside cells). He insists that laboratory tests, which have consistently found sodium benzoate safe at levels used in drinks and food, are outmoded.

In 2000, the World Health Organization reviewed sodium benzoate and concluded that it is safe but noted that the available science upon which this opinion was based was "limited."

Dr. Piper's sensational charge made headlines worldwide and generated calls, especially in Britain, for further investigation. He may be right that modern methods reveal a danger that prior testing couldn't have identified. According to experts at Cornell University, earlier studies have found that 75 to 80 percent of the benzoic acid produced in the body from sodium benzoate is excreted within six hours, and the total dose leaves the body within about 10 hours.

Only very small amounts are used in foods - less than 0.1 percent, not because of any toxicity associated with the preservative but because at higher levels it leaves an undesirable aftertaste.

We'll have to see where further studies lead on this issue. I am more concerned with the effect the excessive consumption of soft drinks has had on the epidemic of childhood obesity. The high fructose corn syrup the drinks contain has potentially disruptive effects on metabolism and may further promote weight gain because it behaves in the body more like fat than glucose, the blood sugar derived from other sweet foods. Fructose in this form may interfere with the process by which the body tells us we are full.

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